Ink supply device for a four color modular printhead

ABSTRACT

An ink supply device for supplying ink to a printhead chip in a printhead assembly. The printchip includes a molding of a settable material, the molding being a two shot molding having a first part of a first material and a second part of a second material. The first part of the molding includes a plurality of collars of a hydrophobic, elastomeric compound which, are releasably engaged with a plurality of ink reservoirs to seal about ink filling formations of said ink reservoirs in the printhead assembly. The second part of the molding may be formed from an Acetal or rigid material.

FIELD OF THE INVENTION

This invention relates to a printhead assembly. More particularly, theinvention relates to a pagewidth inkjet printhead assembly.

SUMMARY OF THE INVENTION

According to the invention there is provided an ink supply device forsupplying ink to a printhead chip, the device including a molding of asettable material, the molding being a two shot molding having a firstpart of a first material and a second part of a second material, whereinthe first part comprises a plurality of collars of a hydrophobic,elastomeric compound which, are releasably engaged with a plurality ofink reservoirs to seal about ink filling formations of said inkreservoirs.

The molding may be a precision injection molding.

The first part may be of an elastomeric material and the second pan maybe of a rigid material.

The second par may be of an Acetal material.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described by way of example with reference to theaccompanying drawings in which:

FIG. 1 shows a three dimensional view, from above, of a printheadassembly, in accordance with the invention;

FIG. 2 shows a three dimensional view, from below, of the assembly;

FIG. 3 shows a three dimensional, exploded view of the assembly;

FIG. 4 shows a bottom view of the assembly;

FIG. 5 shows a three dimensional view, from below, of the assembly withparts omitted;

FIG. 6 shows, on an enlarged scale, an end view of the assembly;

FIG. 7 shows, on the enlarged scale, a sectional end view of theassembly;

FIG. 8 shows a three dimensional, exploded view of a printhead module ofthe assembly;

FIG. 9 shows a bottom view of the module;

FIG. 10 shows a plan view of the module;

FIG. 11 shows a sectional end view of the module taken along line XI—XIin FIG. 10;

FIG. 12 shows a three dimensional, exploded view of an ink reservoir ofthe assembly;

FIG. 13 shows a three dimensional view of a flexible printed circuitboard of the assembly;

FIG. 14 shows a three dimensional, exploded view of a busbar arrangementof the assembly;

FIG. 15 shows a three dimensional view of a multiple printhead assemblyconfiguration; and

FIG. 16 shows, on an enlarged scale, a sectional side view of thebonding of the printhead chip to the TAB film.

DETAILED DESCRIPTION OF THE DRAWINGS

A printhead assembly, in accordance with the invention is designatedgenerally by the reference numeral 10. The assembly 10 uses a pluralityof replaceable printhead modules 12. The advantage of this arrangementis the ability to easily remove and replace any defective modules 12 inthe assembly 10. This eliminates having to scrap an entire printheadassembly 10 if only one module 12 is defective.

The assembly 10 comprises a chassis 14 on which an ink reservoir 16 issecured. The printhead modules 12 are, in turn, attached to thereservoir 16.

Each printhead module 12 is comprised of a microelectromechanical(Memjet) chip 18 (shown most clearly in FIG. 8 of the drawings) bondedby adhesive 20 to a Tape Automated Bond (TAB) film 22, the TAB film 22being electrically connected to the chip 18. The chip 18 and the TABfilm 22 form a sub-assembly 24 which is attached to a micromolding 26.The micromolding 26 is, in turn, supported on a cover molding 28.

Each module 12 forms a sealed unit with four independent ink chambers 30defined in the cover molding 28, the ink chambers 30 supplying ink tothe chip 18. Each printhead module 12 is plugged into a reservoirmolding 32 (shown most clearly in FIGS. 3 and 7 of the drawings) of theink reservoir 16 that supplies the ink. Ten modules 12 butt togetherinto the reservoir 16 to form a complete 8 inch printhead assembly 10.The ink reservoirs 16 themselves are modular, so complete 8 inchprinthead arrays can be configured to form a printhead assembly 10 of adesired width.

The 8 inch modular printhead assembly 10, according to the invention, isdesigned for a print speed and inkflow rate that allows up to 160 pagesper minute printing at 1600 dpi photographic quality. Additionally, asecond printhead assembly, of the same construction, can be mounted in aprinter on the opposite side for double sided high speed printing.

As described above, and as illustrated most clearly in FIG. 8 of thedrawings, at the heart of the printhead assembly 10 is the Memjet chip18. The TAB film 22 is bonded on to the chip 18 and is sealed with theadhesive 20 around all edges of the chip 18 on both sides. This formsthe core Memjet printhead chip sub-assembly 24.

The sub-assembly 24 is bonded on to the micromolding 26. This molding 26mates with the TAB film 22 which, together, form a floor 34 (FIG. 11) ofthe ink chambers 30 of the cover molding 28. The chambers 30 open in aflared manner in a top 36 of the cover molding 28 to define fillingfunnels 38. A soft elastomeric, hydrophobic collar 40 is arranged aboveeach funnel 38. The collars 40 sealingly engage with complementaryfilling formations or nozzles 42 (FIG. 7) of the reservoir molding 32 ofthe ink reservoir 16 to duct ink to the chip 18.

Snap details or clips 44 project from the top 36 of the cover molding 28to clip the cover molding 28 releasably to the ink reservoir 16.

The TAB film 22 extends up an angled side wall 46 of the cover molding28 where it is also bonded in place. The side wall 46 of the covermolding 28 provides the TAB film 22 with a suitable bearing surface fordata and power contact pads 48 (FIG. 8).

The sub-assembly 24, the micromolding 26 and the cover molding 28together form the Memjet printhead module 12. A plurality of theseprinthead modules 12 snap fit in angled, end-to-end relationship on tothe ink reservoir 16. The reservoir 16 acts as a carrier for the modules12 and provides ink ducts 52 (FIG. 7) for four ink colors, Cyan,Magenta, Yellow and blacK (CMYK). The four ink colors are channelledthrough the individual funnels 38 of the cover molding 28 into eachprinthead module 12.

The printhead modules 12 butt up to one another in an overlapping,angled fashion as illustrated most clearly in FIGS. 2 and 4 of thedrawings. This is to allow the Memjet chips 18 to diagonally overlap inorder to produce continuous printhead lengths from 0.8 inches to 72inches (for wide format printers) and beyond.

The Memjet chip 18 is 21.0 mm long×0.54 mm wide and 0.3 mm high. Aprotective silicon nozzle shield that is 0.3 mm high is bonded to theupper surface of the Memjet chip 18.

Each Memjet nozzle includes a thermoelastic actuator that is attached toa moving nozzle assembly. The actuator has two structurally independentlayers of titanium nitride (TiN) that are attached to an anchor on thesilicon substrate at one end and a silicon nitride (nitride) leverarm/nozzle assembly at the other end. The top TiN or “heater” layerforms an electrical circuit which is isolated from the ink by nitride.The moving nozzle is positioned over an ink supply channel that extendsthrough the silicon substrate. The ink supply channel is fluidicallysealed around the substrate holes periphery by a TiN sealing rim. Inkejection is prevented between the TiN rim and the nitride nozzleassembly by the action of surface tension over a 1 micron gap.

A 1 microsecond 3V, 27 mA pulse (85 nanoJoules) is applied to theterminals of the heater layer, increasing the heater temperature byJoule heating. The transient thermal field causes an expansion of theheater layer that is structurally relieved by an “out of plane”deflection caused by the presence of the other TiN layer.

Deflection at the actuator tip is amplified by the lever arm and forcesthe nozzle assembly towards the silicon ink supply channel. The nozzleassembly's movement combines with the inertia and viscous drag of theink in the supply channel to generate a positive pressure field thatcauses the ejection of a droplet.

Memjet actuation is caused by a transient thermal field. The passive TiNlayer only heats up by thermal conduction after droplet ejection.Thermal energy dissipates by thermal conduction into the substrate andthe ink, causing the actuator to return to the ‘at rest’ position.Thermal energy is dissipated away from the printhead chip by ejecteddroplets. The drop ejection process takes around 5 microseconds. Thenozzle refills and waste heat diffuses within 20 microseconds allowing a50 KHz drop ejection rate.

The Memjet chip 18 has 1600 nozzles per inch for each color. This allowstrue 1600 dpi color printing, resulting in full photographic imagequality. A 21 mm CMYK chip 18 as 5280 nozzles. Each nozzle has a shiftregister, a transfer register, an enable gate, and a rive transistor.Sixteen data connections drive the chip 18.

Some configurations of Memjet chips 18 require a nozzle shield. Thisnozzle shield is a micromachined silicon part which is wafer bonded tothe front surface of the wafer. It protects the Memjet nozzles fromforeign particles and contact with solid objects and allows thepackaging operation to be high yield.

The TAB film 22 is a standard single sided TAB film comprised ofpolyimide and copper layers. A slot accommodates the Memjet chip 18. TheTAB film 22 includes gold plated contact pads 48 that connect with aflexible printed circuit board (PCB) 54 (FIG. 13) of the assembly 10 andbusbar contacts 56 (FIG. 14) of busbars 58 and 60 of the assembly 10 toget data and power respectively to the chip 18. Protruding bond wiresare gold bumped, then bonded to bond pads of the Memjet chip 18.

The junction between the TAB film 22 and all the chip sidewalls hassealant applied to the front face in the first instance. Thesub-assembly 24 is then turned over and sealant is applied to the rearjunction. This is done to completely seal the chip 18 and the TAB film22 together to protect electrical contact because the TAB film 22 formsthe floor 34 of the ink chambers 30 in the printhead module 12.

The flexible PCB 54 is a single sided component that supplies the TABfilms 22 of each printhead module 12 with data connections throughcontact pads, which interface with corresponding contacts 48 on each TABfilm 22. The flex PCB 54 is mounted in abutting relationship with theTAB film 22 along the angled sidewall 46 of the cover molding 28. Theflex PCB 54 is maintained in electrical contact with the TAB film 22 ofeach printhead module 12 by means of a pressure pad 62 (FIG. 7). The PCB54 wraps underneath and along a correspondingly angled sidewall 64 ofthe ink reservoir molding 32 of the ink reservoir 16. The part of thePCB 54 against the sidewall 64 carries a 62 pin connector 66.

The sidewall 64 of the ink reservoir molding 32 of the ink reservoir 16is angled to correspond with the sidewall 32 of the cover molding 16 sothat, when the printhead module 12 is mated to the ink reservoir 16, thecontacts 48 of the TAB film 22 wipe against those of the PCB 54. Theangle also allows for easy removal of the module 12. The flex PCB 54 is‘sprung’ by the action of the deformable pressure pad 62 which allowsfor positive pressure to be applied and maintained between the contactsof the flex PCB 54 and the TAB film 22.

The micromolding 26 is a precision injection molding made of an Acetaltype material. It accommodates the Memjet chip 18 (with the TAB film 22already attached) and mates with the cover molding 28.

Rib details 68 (FIG. 8) in the underside of the micromolding 26 providesupport for the TAB film 22 when they are bonded together. The TAB film22 forms the floor 34 of the printhead module 12, as there is enoughstructural integrity due to the pitch of the ribs 68 to support aflexible film. The edges of the TAB film 22 seal on the underside wallsof the cover molding 28.

The chip 18 is bonded on to 100 micron wide ribs 70 that run the lengthof the micromolding 26. A channel 72 is defined between the ribs 70 forproviding the final ink feed into the nozzles of the Memjet chip 18.

The design of the micromolding 26 allows for a physical overlap of theMemjet chips 18 when they are butted in a line. Because the Memjet chips18 now form a continuous strip with a generous tolerance, they can beadjusted digitally to produce the required print pattern, rather thanrelying on very close tolerance moldings and exotic materials to performthe same function. The pitch of the modules 12 is 20.33 mm.

The micromolding 26 fits inside the cover molding 28, the micromolding26 bonding on to a set of vertical ribs 74 extending from the top 36 ofthe cover molding 28.

The cover molding 28 is a two shot, precision injection molding thatcombines an injected hard plastic body (Acetal) with soft elastomericfeatures (synthetic rubber). This molding interfaces with thesub-assembly 24 bonded to the micromolding 26. When bonded into placethe base sub-assembly, comprising the sub-assembly 24 and themicromolding 26, mates with the vertical ribs 74 of the cover molding 28to form the sealed ink chambers 30.

As indicated above, an opening of each chamber 30 is surrounded by oneof the collars 40. These soft collars 40 are made of a hydrophobic,elastomeric compound that seals against the ink nozzles 42 of the inkreservoir 16. The snap fits 44 on the cover molding 28 locate the module12 with respect to the ink reservoir 16.

The ink reservoir 16 comprises the ink reservoir molding 32 and a lidmolding 76 (FIG. 7). The molding 32 is a simple four chamber injectionmolding with the lid molding 76 that is bonded on top to form a sealedenvironment for each color ink. Ink supply pipes 78 (FIG. 12) arearranged at one end of the lid molding 76 to communicate with inkchannels 80 defined in the reservoir molding 32. Labyrinthine,hydrophobic air holes 82 are defined at an opposed end of the lidmolding 76. The air holes 82 are included for bleeding the channels 80during charging. These holes 82 are covered over with a self adhesivefilm 84 after charging.

The lid molding 76 has heat stakes 88, (pins that are designed to meltand hold the molding onto another part) which position and secure theink reservoir 16 to the punched, sheet metal chassis 14. Additional heatstakes 90 are arranged along the reservoir molding 32. These stakes areshown after deformation in FIG. 1 of the drawings once the ink reservoir16 has been secured to the chassis 14.

Receiving formations 92 are defined along the sides of the reservoirmolding 32 for releasably receiving the clips 44 of the printheadmodules 12.

As previously described, the sidewall 64 on the side of the reservoirmolding 32 provides a mounting area for the flexible PCB 54 and dataconnector 66. The reservoir molding 32 also carries details forfacilitating the accurate mounting of the V− and V+ busbars 58 and 60,respectively.

The metal chassis 14 is a precision punched, folded and plated metalchassis used to mount the printhead assembly 10 into various products.The ink reservoir 16 is heat staked to the chassis 14 via the heatstakes 88 and 90. The chassis 14 includes a return edge 94 formechanical strength. The chassis 14 can be easily customized forprinthead mounting and any further part additions. It can also beextended in length to provide multiple arrays of printhead assemblies 10for wider format printers.

Slots 97 are defined in the chassis 14 for enabling access to be gainedto the clips 44 of the modules 12 to release the modules 12 from the inkreservoir 16 for enabling replacement of one or more of the modules 12.

Thin finger strip metallic strip busbars 58 and 60 conduct V− and V+,respectively, to the TAB film 22 on each printhead module 12. The twobusbars 58 and 60 are separated by an insulating strip 96 (FIG. 14). Theflexible, finger-like contacts 56 are arranged along one side edge ofeach busbar 58, 60. The contacts 56 electrically engage the relevantcontact pads 48 of the TAB film 22 of each module 12 for providing powerto the module 12. The contacts 56 are separated by fine rib details onthe underside of the ink reservoir molding 32.

A busbar sub-assembly 98, comprising the busbars 58, 60 and theinsulating strip 96 is mounted on the underside of the sidewall 64 ofthe reservoir molding 32 of the ink reservoir 16. The sub-assembly isheld captive between that sidewall 64 and the sidewall 46 of the covermolding 28 by the pressure pad 62.

A single spade connector 100 is fixed to a protrusion 102 on the busbar58 for ground. Two spade connectors 104 are mounted on correspondingprotrusions 106 on the busbar 60 for power. The arrangement is suchthat, when the sub-assembly 98 is assembled, the spade connectors 104are arranged on opposite sides of the spade connector 100. In this way,the likelihood of reversing polarity of the power supply to the assembly10, when the assembly 10 is installed, is reduced. During printheadmodule 12 installation or replacement, these are the first components tobe disengaged, cutting power to the module 12.

To assemble the printhead assembly 10, a Memjet chip 18 is dry tested inflight by a pick and place robot, which also dices the wafer andtransports individual chips 18 to a TAB film bonding area. When a chip18 has been accepted, a TAB film 22 is picked, bumped and applied to thechip 18.

A slot in the TAB film 22 that accepts the chip 18 and has the adhesive20, which also functions as a sealant, applied to the upper and lowersurfaces around the chip 18 on all sides. This operation forms acomplete seal with the side walls of the chip 18. The connecting wiresare potted during this process.

The Memjet chip 18 and TAB film 22 sub-assembly 24 is transported toanother machine containing a stock of micromoldings 26 for placing andbonding. Adhesive is applied to the underside of the fine ribs 70 in thechannel 72 of the micromolding 26 and the mating side of the undersideribs 68 that lie directly underneath the TAB film 22. The sub-assembly24 is mated with the micromolding 26.

The micromolding sub-assembly, comprising the micromolding 26 and thesub-assembly 24, is transported to a machine containing the covermoldings 28. When the micromolding sub-assembly and cover molding 28 arebonded together, the TAB film 22 is sealed on to the underside walls ofthe cover molding 28 to form a sealed unit. The TAB film 22 furtherwraps around and is glued to the sidewall 46 of the cover molding 28.

The chip 18, TAB film 22, micromolding 26 and cover molding 28 assemblyform a complete Memjet printhead module 12 with four sealed independentink chambers 30 and ink inlets 38.

The ink reservoir molding 32 and the cover molding 76 are bondedtogether to form a complete sealed unit. The sealing film 84 is placedpartially over the air outlet holes 82 so as not to completely seal theholes 82. Upon completion of the charging of ink into the ink reservoir16, the holes 82 are sealed by the film 84. The ink reservoir 16 is thenplaced and heat staked on to the metal chassis 14.

The full length flexible PCB 54 with a cushioned adhesive backing isbonded to the angled sidewall 64 of the ink reservoir 16. The flex PCB54 terminates in the data connector 66, which is mounted on an externalsurface of the sidewall 64 of the ink reservoir 16.

Actuator V− and V+ connections are transmitted to each module 12 by thetwo identical metal finger strip busbars 58 and 60. The busbarsub-assembly 98 is mounted above the flex PCB 54 on the underside of thesidewall 64 of the ink reservoir molding 32. The busbars 58, 60 and theinsulating strip 96 are located relative to the ink reservoir molding 32via pins (not shown) projecting from the sidewall 64 of the inkreservoir molding 32, the pins being received through locating holes 108in the busbars 58, 60 and the insulating strip 96.

The Memjet printhead modules 12 are clipped into the overhead inkreservoir molding 32. Accurate alignment of the module 12 to thereservoir molding 32 is not necessary, as a complete printhead assembly10 will undergo digital adjustment of each chip 18 during final QAtesting.

Each printhead module's TAB film 22 interfaces with the flex PCB 54 andbusbars 58, 60 as it is clipped into the ink reservoir 16. To disengagea printhead module 12 from the reservoir 16, a custom tool is insertedthrough the appropriate slots 97 in the metal chassis 14 from above. Thetool ‘fingers’ slide down the walls of the ink reservoir molding 32,where they contact the clips 44 of the cover molding 28. Furtherpressure acts to ramp the four clips 44 out of engagement with thereceiving formations 92 and disengage the printhead module 12 from theink reservoir 16.

To charge the ink reservoir 16 with ink, hoses 110 ( FIG. 3) areattached to the pipes 78 and filtered ink from a supply is charged intoeach channel 80. The openings 82 at the other end of the ink reservoircover molding 76 are used to bleed off air during priming. The openings82 have tortuous ink paths that run across the surface, which connectthrough to the internal ink channels 80. These ink paths are partiallysealed by the bonded transparent plastic film 84 during charging. Thefilm 84 serves to indicate when inks are in the ink channels 80, so theycan be fully capped off when charging has been completed.

For electrical connections and testing, power and data connections aremade to the flexible PCB 54. Final testing then commences to calibratethe printhead modules 12. Upon successful completion of the testing, theMemjet printhead assembly 10 has a plastic sealing film applied over theunderside that caps the printhead modules 12 and, more particularly,their chips 18, until product installation.

It is to be noted that there is an overlap between adjacent modules 12.Part of the testing procedure determines which nozzles of theoverlapping portions of the adjacent chips 18 are to be used.

As shown in FIG. 15 of the drawings, the design of the modular Memjetprinthead assemblies 10 allows them to be butted together in anend-to-end configuration. It is therefore possible to build a multipleprinthead system 112 in, effectively, unlimited lengths. As long as eachprinthead assembly 10 is fed with ink, then it is entirely possible toconsider printhead widths of several hundred feet. This means that theonly width limit for a Memjet printer product is the maximummanufacturable size of the intended print media.

FIG. 15 shows how a multiple Memjet printhead system 112 could beconfigured for wide format printers. Replaceable ink cartridges 114, onefor each color, are inserted into an intermediate ink reservoir 116 thatalways has a supply of filtered ink. Hoses 118 exit from the undersideof the reservoir 118 and connect up to the ink inlet pipes 78 of eachprinthead assembly 10.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

We claim:
 1. An ink supply assembly for supplying ink to an elongateprinthead that includes at least one printhead chip, the assemblycomprising ink reservoirs, each ink reservoir defining a number ofchannels, each channel being configured to contain an ink of aparticular color, and each ink reservoir having a number of fillingformations, each filling formation being in fluid communication with arespective channel; and ink supply devices that each comprise a moldingof a settable material, the molding being a two shot molding having afirst part of a first material and a second part of a second material,wherein the first part comprises a plurality of collars of ahydrophobic, elastomeric compound which are configured to be sealinglyand releasably engageable with respective ink filling formations of saidink reservoirs, and the second part defines a number of ink chambers,each ink chamber being configured to contain ink of a particular colorand being in fluid communication with a respective ink channel of oneink reservoir via one collar.
 2. An ink supply device for supplying inkto an elongate printhead that includes at least one printhead chip, froma number of reservoirs, each reservoir defining a number of channels,each channel being configured to contain an ink of a particular color,and each ink reservoir having a number of filling formations, eachfilling formation being in fluid communication with a respectivechannel, the device comprising ink supply devices that each comprise amolding of a settable material, the molding being a two shot moldinghaving a first part of a first material and a second part of a secondmaterial, wherein the first part comprises a plurality of collars of ahydrophobic, elastomeric compound which are configured to be sealinglyand releasably engageable with respective ink filling formations of saidink reservoirs, and the second part defines a number of ink chambers,each ink chamber being configured to contain ink of a particular colorand being in fluid communication with a respective ink channel of oneink reservoir via one collar.